This invention relates generally to bulk storage facility for pulverulent, friable, granular or fungible material such as coal, mineral ore, grain or the like. In particular, this invention concerns a bulk storage facility in which a material storage slot, defined by a pair of convergent inclined walls, has interlocking facing panels which cover internally stabilized earth walls.
A typical bulk storage facility includes a material storage slot defined by generally planar inclined walls which are convergent toward a longitudinal opening at the bottom. The longitudinal opening communicates with a reclaim tunnel running longitudinally of the storage slot below the longitudinal opening. A pair of endwalls, either vertical or inclined, complete the definition of the storage slot. The endwalls extend between the inclined walls.
To protect the bulk material being stored from environmental moisture, a roof typically covers the storage slot. The roof is often A-shaped in cross section with a suitable conventional tripper conveyor extending longitudinally of the roof at the apex thereof. Bulk material is introduced into the storage slot with the tripper conveyor and is removed from the storage slot by a reclaim conveyor positioned in the reclaim tunnel.
In the past, bulk storage facilities have been used, for example, in the storage of coal since the bulk storage facility is particularly well adapted for use near coal mining operations such as those in the Western United States were sub-bituminous coal is mined. Since sub-bituminous coal does not have a reliable energy rating (as BTU available per pound of material), it is desirable to blend the coal after mining and before use. In a typical bulk storage facility, material is stocked horizontally and removed vertically so that blending occurs. Thus, the desirable blending of sub-bituminous grades of coal is conveniently effected.
The desired location for a bulk storage facility has an influential effect on basic design considerations. For example, where the local terrain is flat, the storage slot may be constructed either by excavation below the existing ground surface or by building parallel dikes above the existing ground surface. In rugged terrain, the storage slot is often constructed adjacent to a convenient hillside by extending the hillside to define one inclined wall of the slot and by building a parallel dike to define the second inclined wall.
Within the bulk storage facility, the inclined walls of the storage slot are inclined relative to horizontal by an angle which exceeds the classical angle of repose for the bulk material to be stored so that there are no dead areas from which material does not discharge.
In the past, where the angle of the inclined walls was low, i.e., less than 45.degree., the conventional construction method was to compact the slope material and then trim the inclined slope to the proper surface shape. Trimming was typically effected by a bulldozer with a tilting blade or by a drag line. Once the slope surface was prepared by trimming, a facing was applied in one of several alternative manners: placing precast concrete panels; in situ casting of concrete facing slabs; or, recently, by spraying a gunite facing.
When the angle of the inclined walls is comparatively high, e.g. 45.degree. or greater, the compacted slope material has marginal stability. Accordingly, more complex construction techniques were required. For example, a facing of cement stabilized or lime stabilized material was positioned adjacent the storage slot so as to extend in the neighborhood of fifteen feet away from the surface toward the compacted material. The stabilized zone was placed as each layer of the associated dike or hillside extension was deposited and compacted.
The large size of a bulk storage facility in combination with the vagaries of construction techniques cause contractors to overbuild the stabilized zone into the storage slot so that the proper lateral depth for the stabilized zone is ensured. The overbuilt portion then was trimmed to the proper inclination before a facing was applied; however, while the cement or lime stabilization stabilized the inclined slope, it also was hard to cut during the subsequent trimming operation. Moreover, the stabilization technique was expensive due to the additional material, i.e., cement or lime, that was required and was very time consuming.
After the compacted slope material was stabilized, the trimming operation began at the top of the inclined wall by cutting the stabilized zone to proper grade for a selected depth, or bench. Then, welding wire reinforcing fabric was applied and a gunite facing was subsequently applied. Then, another lower bench was shaped and faced and so on until the wall was finished. Some contractors elected, as an alternative, to cut the entire slope surface before applying the reinforcing fabric and gunite.
With inclined walls having either high or low angles, the reclaim conveyor tunnel was generally built first. Then, the tunnel was filled with earthen material before the inclined walls were built. In fact, during conventional construction of the storage facility, an enormous quantity of earthen material was placed in the storage slot to facilitate construction which material was later removed before the facility was complete. The presence of this earthen material precluded any work on installation of the reclaim conveyor in the reclaim tunnel until the inclined walls had been completed. It is noted also that during trimming operations discussed above, the trimmed material often dropped into the then untrimmed portion of the storage slot.
In addition to the problems discussed above, the construction of a bulk storage facility heretofore has been plagued with other problems. For example, the overburden material often present at existing sites for bulk storage facilities and used for the earthen dikes is not always well-suited for cement or lime stabilization. Sometimes, the amount of cement or lime required for stabilization cannot be predicted with any meaningful degree of certainty. Thus, the cost of additional stabilizing material cannot be realistically estimated.
Moreover, since trimming of the inclined slopes is generally performed by construction equipment, such as bulldozer, the trimmed surface is not highly uniform. As a result the quantity of gunite material that needs to be applied is difficult to evaluate. In this connection, cost overruns for gunite material alone frequently run in the vicinity of 50 to 100%.
Furthermore, with respect to the gunite facing, the quality of the surface is a strong function of nozzle orientation relative to the surface: the best surface results from the nozzle being normal to the surface. Thus, the day-to-day attitude of workmen applying the surface can affect surface quality.
With the existing construction techniques, as much as a year may be required to complete construction of a storage facility. When climatic conditions require a cessation of construction activities, e.g., during winter the surface water erosion of prepared slope surfaces can require repair of those surfaces before construction continues, further delaying construction completion.
Accordingly, it is apparent that there exists a need for an economical, practical method and apparatus for constructing inclined slope walls such as those used in a bulk storage facility.